In the case where a disaster such as a large earthquake occurs, there may occur a situation in which an infrastructure of a wide area communication such as a cellular network or an Internet access network breaks down or congestion of the communication occurs so that the communication cannot be performed. When such a situation occurs, it becomes impossible to contact a sufferer so that the safety of the sufferer cannot be ascertained. In order to cope with this situation, a system for transmitting safety information at the time of disaster is studied and developed.
PTL 1 discloses a system in which safety information is exchanged between information communication terminals such as cellular phones and notebook computers, and the safety information is thereby propagated to a surrounding area. However, the propagation of the information via direct communication between the information communication terminals results in slow spreading speed of the information and narrow spread area. This is particularly due to the fact that the communication range of the direct communication by the information communication terminal is narrow and the fact that the sufferer cannot move a long distance.
PTL 2 discloses a system that allows acquisition of information even in an environment in which a communication infrastructure is not provided, though it does not take account of disaster occurrence. In PTL 2, the current position and destination of a vehicle are managed and, in the case where a first vehicle travels to the destination where the communication infrastructure is not provided, selected is a second vehicle which becomes capable of communicating with the first vehicle by a vehicle-to-vehicle communication before the first vehicle reaches the destination, and information related to the destination of the first vehicle is transmitted to the second vehicle. With this, the first vehicle can acquire the information related to the destination via the second vehicle. However, it is difficult to implement a process of grasping the current positions and the destinations of all vehicles at the time of disaster, and the system cannot be used without alteration as a safety information transmission method at the time of disaster.